Double-acting hydraulic jack



April 19, 1960 K. TRUMPER ETAI- DOUBLE-ACTING HYDRAULIC JACK Filed Aug. 12, 1958 Inventors. ,m/xeyo 7202/12? :51 /x saws/05.? 2 $434M Jt States Patent'O DQUBLE-ACTING HYDRAULIC llACK Konrad Triirnper, Weideuau (Sieg), and Felix Schneider, Dreis-Tiefcnbaeh, Kreis Siegen, Germany, assignors to Rheinstahl Siegener Eisenbahnbedarf A31, Dreis Tiefenbach, Kreis Siegen, Germany Application August 12, 1958, Serial No. 754,648

7 Claims. (Cl. 121-46) The present invention relates to hydraulic lifting devices in general, and more particularly to a double-acting, multi-stage telescopic jack.

Single-acting multi-stage hydraulic jacks of known construction comprise a series of cylinders which are tele-- scoped into each other and whose mantles define longitudinal bores, the upper ends of bores opening into the interior of respective cylinders and their lower ends communicating with the exterior of the cylinders. When the so constructed jack is fully expanded, the bores constitute a continuous channel for the passage of pressure medium from the interior of telescoped cylinders. This arrangement prevents damage to the jack in case that the source of pressure, i.e. a hydraulic pump, would continue to sup ply pressure medium into the cylinders after the latter have already performed their full working or expanding stroke.

Certain types of double-acting multi-stage hydraulic jacks of known construction are formed with annular enclosures or spaces between the adjacent cylinders, the enclosures being in communication with each other through channels which extend longitudinally in the mantle of each cylinder. The upper end of each channel opens into the interior of its cylinder while its lower end opens to the exterior of the respective cylinder.

A difierent type of double-acting hydraulic jacks comprises cylinders formed with twin-walled mantles, the annular spaces between the twin walls of each cylinder performing the functions of aforementioned channels. This type of hydraulic jacks is operated by introducing therein a suitable pressure medium, e.g. oil, to act against the bases or end walls of individual cylinders while the pressure medium contained in the annular spaces between the twin walls of cylinder mantles escapes simultaneously with the expanding movement of the cylinders. A disadvantage of such known double-acting jacks is in that the mantle of each cylinder is weakened by the provision Patented Ap 19, 1

of known construction as above described, would necessitate a construction with excessive overall weight and high consumption of pressure medium.

An important object of the present invention is to provise an improved double-acting, multi-stage hydraulic jack which is constructed with a view to keep its overall weight considerably below the weight of similar apparatus of known construction. 7

Another object of the invention is to provide a device of the above described character whose consumption of pressure medium is relatively low, and which is so constructedthat the working and retracting strokes are per: formed at a considerable speed.

. A further object of the invention is to provide a doubleacting hydraulic jack which operates in such manner that the speed of its working or expanding stroke approximates or equals the speed of its retracting or collapsing stroke.

A still further object of the present invention is to provide an improved double-acting hydraulic jack consisting of telescoped cylindrical members which is so constructed that its expanding and/ or retracting speed does not depend upon the changes in volume of pressure chambers defined by its cylinders.

A yet further object of the invention is to provide a device as above set forth which is so constructed that the ofannular spaces or bores therein. This is particularly felt because the pressure medium subjects the cylinders to considerable stretching and buckling forces and, therefore, any weakening of cylinder mantles is extremely undesirable. In addition, high pressures prevailing in the channels or annular spaces of such cylinders may bring about deformation often reaching such proportions as to cause improper sealing action of gaskets interposed between the members which slide with respect to each other though it is well known that proper sealing action of gas kets is essential in apparatus of this character. Still further, the provision of bores, channels or annular spaces necessitates the use of cylinders with mantles of considerable thicknesses, which in turn increases the overall weight of a so-constructed jack. The weight problem in hydraulic jacks is particularly acute when such devices are utilized in connection with conveyances for large receptacles, for example, for transferring large receptacles from a railroad car onto a different conveyance or vice versa. For such applications, the working stroke of a double-acting jack should be about 12 feet which, by utilizing devices expanding and retracting strokes are carried out with little loss in time and by utilization of relatively small quantities of pressure medium.

A concomitant object of the invention is to provide a hydraulic jack which is relatively simple in construction, reliable and efficient in operation, and which may comprise a greater or lesser number of telescoped cylinders to vary the overall length of its strokes. i

An additional object of the instant invention is to provide a double-acting multi-stage hydraulic jack whose cylinders comprise mantles without longitudinal channels or annular spaces therein.

The above and certain other objects of the invention are attained by the provision of a device which comprises an outer cylinder, an inner cylinder, and at least one intermediate cylinder which latter is telescoped into the outer cylinder and telescopically receives the inner cylinder. Annular spaces are provided between the tubular walls of adjacent cylinders, each space communicating with the enclosure in the inner cylinder and the outermost space communicating with a source of pressure, Such as a hydraulic pump or the like. The intermediate cylinder or cylinders and the inner cylinder are formed with a base or end wall acting as a piston in the next-larger cylinder, each piston-like base save for that of the inner cylinder supporting a preferably coaxial tubular member or pipe through which the respective annular spaces communicate with the enclosure in the inner cylinder. The outer cylinder has a base or end wall which, with the piston-like base of the largest intermediate cylinder, forms a pressure chamber connected to the source of pressure. The adjacent pistonor plunger-like bases of successive cylinders within the outer cylinder define therebetween additional pressure chambers which communicate with each other and with the pressure chamber in the outer cylinder.

An important feature of the invention is in that the pressure medium filling the annular spaces and the interior of inner cylinder need not be expelled from the jack when the latter performs its working stroke but merely passes from the annular spaces into the inner cylinder.

Another feature of the just-described arrangement is in that lesser amounts of pressure medium are required for the operation of our improved jack while the periods of time required to perform working strokes approxitracting strokes. In fact, while the jack expands, additional pressure medium may be introduced from the source of pressure into the annular spaces and into the interior of the inner cylinder which brings about simultaneous application of pressure and hence a pressure differential at the opposing sides of the base of each slidable cylinder. In other words, pressure maybe applied to both sides of each slidable piston-like base while the jack expands to in such manner reduce the speed of expansion and to bring the collapsing or retracting speed closer to the expanding speed. One can say that, when pressure is applied to both sides of the 'slidable bases, only the pressure differential causes expansion or working stroke of the jack. Such arrangement, in addition to being more economical as regards the overall amounts of pressure medium, is the first one known to inventors in which the speed of expansion may equal orat least approximate the speed at which the jack collapses.

N tubular member is necessary in the base of the inner cylinder because, as will be readily understood upon perusal of the following detailed description of the drawing, the inner cylinder by itself performs, the functions of such tubular members in that its mantle is formed with one or more bores or apertures constituting communicating passages between its interior and the surrounding annular space.

The novel device further comprises suitable control means in the form of valves which permit simultaneous or separate introduction of pressure medium into the annular spaces on the one hand, and into the pressure chambers on the other hand. When the jack is about to collapse, pressure medium is introduced into annular spaces alone while the medium in the pressure chambers is free to flow into a discharge line and thence to the oil sump.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of a. specific embodiment when read in connection with the accompanying drawing in which the improved jack is shown in axial section and in slightly expanded position.

The jack comprises an outer cylinder 1 having an open top and a base 2. Cylinder 1 telescopicallyreceives a second or intermediate cylinder 3 whose base 4 constitutes a piston in member 1, cylinder 3 in turn telescopically receiving a further intermediate cylinder 5 having a base '6 acting as a piston in member 3. Inner cylinder 7 is telescoped into cylinder 5 and is formed with a base 8 acting as a piston in member 5. Internal annular projections 1a, 3a, 5a, each receiving a pair of gaskets 9, are provided at the open ends of members 1, 3 and 5. External gaskets 13 are installed in external annular projections 10, 11, 12 surrounding pistons 4, 6, 8 and forming part of cylinders 3, 5 and 7, respectively. Collars 10,-1.1, 12 thus constitute the peripheral zones of respective pistons or bases 4, 6, 8, each thereof being slidablyreceived in the next larger cylinder; Pistons 4 and 6 are formed with respective bores18, 21 which constitute communicating passages between pressure chambers 19, 20 on the one hand, and pressure chambers 20, 22 on the other hand. Pressure chamber 19 is defined by the tubular wall or mantle of cylinder 1, its base 2 and the piston 4; chamber 20 is formed by pistons 4, 6 and by the mantles of cylinder 3 and a tubular member 14; and the chamber 22 is disposed between the mantle of cylinder 5, its piston-shaped base 6, the piston-like base 8, and the cylindrical mantle of a second tubular member 16.

.Base 4 of second largest cylinder 3 preferably-coaxially supports the aforementioned tubular member 14, .the

mate or equal the periods required for collapsing or re pistons or bases 6 and 8.

other tubular member 16 being supported by the base 6-of the other intermediate cylinder 5. Tubular member or pipe 14 is slidably received in a bore provided in the base 6 of cylinder 5, while the other tubular member or pipe 16 extends through a bore in the base 3 of inner cylinder 7 and coaxially surrounds a portion of member 14. Gaskets 15 in the base 6 prevent passage of pressure medium between chamber 26 and the interior of pipe 16, similar gaskets or sealing means 17 preventing the fiow of pressure medium between chamber 22 and an enclosure 2? within the innermost cylinder 7 The length of pipes 14, 16 is so selected that it at least somewhat exceeds the length of strokes performed by respective The mantles or cylinders .1 and 3 define therebetween a variable annular pressure space orenclosure 23 extending between external annular projection 16 of member 3 and the internal annular projection 11a at the upper end of member 1. A similar variable annular space 24 is formed between the mantles of cylinders '3, 5 and sleeves 11, 3a; while the mantles of cylinders 5, 7 together with sleeves 12, 5a define therebetween a third variable annular space 25. Annular space23 communicates with the interior of inner tubular member or pipe 14 .andhence with chamber or enclosure 29 througha channel 26 provided in the outer sleeve 19 and base 4 of cylinder 3. Annular space 24, on the other hand, communicates with the interior of tubular member 16 and thereover with enclosure 29 through a channel 27 provided in the outer collar 11 and the base 6 of cylinder 5. At least one transverse bore 28 in the tubular wall of inner cylinder 7 constitutes a communicating passage between the annular .space 25 and enclosure 29. I

The end of inner cylinder 7 extending through projection 5a at the open end of intermediate cylinder '5 is closed .by a plate 30a which, with a similar plate 30b defines a cylindrical spaceGlP receiving the piston 31a of alug or eye 31. If desired, a hydraulic fluid may beintroduced into the space 36 to reciprocate piston 31:: and to thereby displace the lug '31 with respect to the inner cylinder 7. .It will be understood that a mechanicalactuating device may replace the piston 31a in order to cause sliding movements of lug 31 with respect to member 7. i

{k :pressure line or conduit 33 ;is fixed to the outer cylinder 1 in the proximity of the latters sleeve It: by means of a connecting element 32, the line communicatmg with one extremity of the annular space 23. vA second conduit or line .35 is fixed to the base 2 by,.a connecting device 34 and communicates with the pressure chamber 19 in cylinder '1. Lines 33 and 35 lead into a valve housing 36 which also receives the discharge end of a supply line 37 leading to a source of pressure, e.g. a hydraulic pump 42, and one end of a discharge pipe 41 leading to the oil sump, not shown. Valve 38 controls the how of pressure medium into and from line 33, and' a similar valve 39 controls the flow of pressure medium from supply pipe 37 into the line 35. A third into :lines 33 and 35. Oil flowing through line 35 into chamber 19 moves piston 4- and hence the larger intermediate cylinder 3 away from base 2 while at the same time :passing through bore 18 into the pressure chamber 20 and therefrom through bore 21 into the chamber 22. In this 'manner, slidable cylinders 3, 5, 7 are displaced not only with respect to stationary outer cylinder 1 "but also with respect to each other. Maximum strokes of slidable cylinders 3, 5 and 7 are determined by the position of internal sleeves 1a, 3a, 5a which act as abutments or stops against the outwardly advancing external sleeves 10, 11, 12, respectively. It will thus be noted that the pressure medium passing through line 35 in the direction of chamber 19 by itself causes displacement of cylinders 3, 5, 7 by acting against respective pistons or bases 4, 6 and 8. Ir valve 38 would remain closed, the volume of the displaced medium in annular spaces 23, 24, 25 could have to be exactly thesame as the volume (tubular members 14, 16) by which space 29 is increased by operation of the cylinders. If this were the case, complete movement of the cylinders would be possible. r

However, valves 38 and 39 are normally open during movement of the cylinders, so that communication takes place, and the displaced volume is greater, so that the medium, passing through line 33, valves 38, 39, and line 35 further increases the speed at which the jack expends. if lines 33 and 35 are simultaneously connected to line 37, the efiective working surfaces of pistons 4, 6 and 8 are reduced by the cross-sectional areas of respective annular spaces 23, 24 and 25, because the pressure of medium in spaces 23-25 is opposed to that of medium in chambers 19, 20 and 22. This pressure differential, however, is utilized for reduction in the overall quantity of pressure medium required forfull expansion and for equalizing the speed of expansion and contraction.

It will be noted that each slidable cylinder with the exception of the innermost one carries a tubular member. The innermost cylinder 7 need not carry a member corresponding to parts 14, 16 because said cylinder actually performs the functions of such tubular members.

When it is desired to collapse the jack, valves 38 and 40 are opened and the valve 39 closed. The oil entering through line 33 into annular spaces 23-25 causes cylinders 3, 5 and 7 to perform a return stroke toward the base 2, while the pressure medium flowing from chamber 19 into line 35 escapes through open valve 40 into the discharge pipe 41. While the jack collapses, pressure medium acts against the surfaces of annular projections 10, 11, 12 in respective annular spaces 23, 24 and 25, as well as against the exposed end faces of tubular members 14, 16 in enclosure 29 within the inner tube 7, and in this manner causes the back flow of oil through line 35. superfluous oil fiows from chamber 22 through bore 21 into chamber 20 and thence through bore 18 into chamber 19 to escape through line 35 and over valve 40 into discharge line 4i.

The number of intermediate cylinders, i.e. of those corresponding to members 3 and 5 in the illustrated embodiment, may be reduced to one or increased to three or more, the number of such intermediate cylinders depending upon the desired total stroke of the jack and upon intended use of the device. Each intermediate cylinder carries a tubular member connecting the annular space which surrounds its mantle with the enclosure within the innermost cylinder. The operation of the improved jack is analogous regardless of the number of intermediate cylinders.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic and specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

We claim:

1. A double-acting hydraulic jack, comprising in combination: an outer cylinder having a base, a mantle, and an open end; an inner cylinder having a base defining a bore, a closed end, a mantle, and an enclosure therewithin; an intermediate cylinder having a base defining a bore and being slidably received in themantle of said outer cylinder, an open end, and a mantle slidably re ceiving the base of said inner cylinder, said last mentioned mantle defining a first enclosed annular space with the mantle of said outer cylinder which extends between the base of, said intermediate cylinder and the open end of said outer cylinder, and a second enclosed annular space with the mantle of said inner cylinder which extends between the base of said inner cylinder and the open end of said intermediate cylinder; the mantle of said inner cylinder having at least one aperture constituting a communicating passage between said second annular space and the enclosure in said inner cylinder; a tubular member having one end fixed to the base of said intermediate member, extending through the bore in the base of said inner cylinder, and having an open end extending into the enclosure in said inner cylinder; the base of said intermediate cylinder defining a channel communicating with said first annular space and with the interior of said tubular member; said last mentioned base defining with the base of said outer cylinder a first pressure chamber, and with the base of said inner cylinder at second pressure chamber communicating with said first pressure chamber through the bore in the base of said intermediate cylinder; a source of pressure medium; and conduit means for connecting said source with said first annular space and with said first pressure chamber.

2. A double-acting, multi-stage hydraulic jack, coinprising, in combination: an outer cylinder having a base, a mantle, and an open end; an inner cylinder having a base defining a bore, a closed end, a mantle, and an enclosure therewithin; a first intermediate cylinder having a base defining a bore and slidably received in the mantle of said outer cylinder, an open end, and a mantle; a second intermediate cylinder having a base defining a bore and slidably received in the mantle of said first intermediate cylinder, an open end, and a mantle slidably receiving the base of said inner cylinder; the mantles of said outer cylinder and of said first intermediate cylinder defining therebetween a first enclosed annular space extending between the base of said first intermediate cylinder and the open end of said outer cylinder; the mantles of said first and of said second intermediate cylinder defining therebetween a second enclosed annular space extending between the base of said second intermediate cylinder and the open end of said first intermediate cylinder; the mantles of said second intermediate cylinder and of said inner cylinder defining therebetween a third enclosed annular space extending between the base of said inner cylinder and the open end of said second intermediate cylinder; a first tubular member having one end fixed to the base of said first intermediate cylinder, slidably extending through the base of said second intermediate cylinder and having an open end in the enclosure in said inner cylinder; a second tubular member having one end fixed to the base of said second intermediate cylinder, slidably extending through the bore in the base of said inner cylinder in surrounding relation about said first tubular member, and having an open end in the enclosure in said inner cylinder; the bases of said first and said second intermediate cylinder defining channels constituting communicating passages between said first and said second annular space and the interior of said first and said second tubular member, respectively; the mantle of said inner cylinder having at least one aperture constituting a communicating passage between said third annular space and the enclosure in said inner cylinder; the bases of said outer cylinder and of said first intermediate cylinder defining therebetween a first pressure chamber; the bases of said first and of said second intermediate cylinder defining therebetween a second pressure chamber communicating with said first pressure chamber through the bore in the base of said first intermediate cylinder; the bases of said second intermediate cylinder and of said inner cylinder defining therebetween a third pressure chamber communicating with .said ,second pressure chamber through the bore in the base of said second intermediate cylinder; at source of pressure medium; and conduit means for connecting said source to said first annular space and to said first pressure chamber.

3,. A double-acting, multi-stage hydraulic jack, comprising, in combination: an outer cylinder having a base, a mantle, and an open end; an inner cylinder having a base defining a bore, a closed end,. a mantle, and an enclosure therewithin; a first intermediate cylinder having a base defining a bore and slidably received in the mantle of said outer cylinder, an open end, and a mantle; a second intermediate cylinder having a base defining a bore and slidably received in the mantle of saidfirst intermediate cylinder, an open end, and a mantle slidably re ceiving the base of said inner cylinder; the mantles of said ,oute'r cylinder and ofisaid first intermediate cylinder defining therebetween a first enclosed annular spaceextend ng between the :base of said first intermediate cylinder and the open end of saidtoutert cylinder; the mantles of ,said first and of said second intermediate cylinder defining therebetween a second enclosed annular space extending between the base of said second intermediate cylinder and the open end of said first intermediate cylinder; the mantles of said second intermediate cylinder and of said inner cylinder defining therebetween .a third enclosed annular space extending between the base of said inner cylinder and the open end of said second intermediate cylinder; a first tubular member having one end fixed to the base of said first intermediate cylinder, slidably extending through the base of said second intermediate cylinder and having an open end in the enclosure in said inner cylinder; a second tubular member having .one end fixed to the base of said second intermediate cylinder, slidably extending through the bore in the base ofsaid inner cylinder insurrounding relation about said first tubular member, and having an open end inthe enclosure in said inner cylinder; the bases of said first and said second intermediate cylinder defining channels constituting communicating passages between said first and said second annular space and the interior of said first and said second tubular member, respectively; the mantle of said inner cylinder having at least one aperture constituting a communicating passage between said third annularspace and the enclosure in said inner cylinder; the bases of said outer cylinder and of said first intermediate cylinder defining therebetween a first'pressure chamber; the bases of .said first and of said-second intermediate cylinder defining therebetween a second pressure chamber communicating with said first pressure chamber through the bore in the baseof said first intermediate cylinder; the bases of said second intermediate cylinder and of said inner cylinder defining therebetween a third pressure chamber communicating with said second pressure chamber through the bore in the base of said second intermediate cylinder; a source of pressure medium; conduit means for connecting said source to said first annular space and to said first pressure chamber; and valve means in said conduit means for controlling the flow of pressure medium from said source into said first annular space and into said first pressure chamber, respectively.

4. A double-actingmulti-stage hydraulic jack comprising, in combination: an outer cylinder having a base, a

mantle, an openend .and an internal projection adjacent to said open end; an inner cylinder having a base defining a bore, an external projection surrounding said base, a mantle defining at least one aperture, a closed end, and an enclosure therewithin; an intermediate cylinder having a base defining a bore, an external projection surrounding said base and slidably received in the mantle of said outer cylinder, at mantle, an open end, and an I internal projection adjacent to said open end and slidably receiving the projection of saidfinner cylinder; the

cs mantles of said outer and .of said intermediate cylinder defining therebetween a first annular space extending be tween the projection of said outer cylinder and the external projection of said intermediate cylinder; the mantles of said intermediate and of said inner cylinder defining therebetween a second annular space extending between the inner projection of said intermediate cylinder and the projection of said inner cylinder and communicating with the enclosure in said inner cylinder through the aperture in the mantle'of said inner cylinder; a tubular member having one end fixed to the base of said intermediate cylinder, slidably extending through the bore in the base of said inner cylinder and having an open end in the enclosure in said inner cylinder; the external projection and the base of said intermediate cylinder defining a channel constituting a communicating passage between said first annular space and the interior of said tubular member; the bases of said outer cylinder and of said intermediate cylinder defining therebetweena first pressure chamber, and the bases of said intermediate and of said inner cylinder defining therebetween a second pressure chamber communicating with the first pressure chamber through the bore in the base of said intermediate cylinder; a source of pressure medium; and

conduit means for connecting said source with said first V annular space and with said first pressure chamber.

5. A double-acting, multi-stage hydraulic jack comprising, in combination: an outer cylinder having a base, a mantle, an open end and an internal projection adjacent to said open end; an inner cylinder having a base defining a bore, an external projection disposed about said base, a closed end, a mantle defining at least one aperture, and an enclosure therewithin; a first intermediate cylinder and a second intermediate cylinder, each intermediate cylinder having a base defining a bore, an external projection surrounding its base, a mantle, an open end, and an internal projection adjacent to its open end; the external projection and the mantle of said first intermediate cylinder beingrslidably received in the mantle and in the internal projection, respectively, of said outer cylinder, and the external projection and the mantle of said second intermediate cylinder being slidably received in the mantle and in the internal projection, respectively, of said first intermediate cylinder, the external projection and the mantle of said inner cylinder being slidably received in the mantle and in the internal projection, respectively, of said second intermediate cylinder; the mantles of said cylinders defining therebetween three annular spaces the first of which extends between the external projection of said first intermediate cylinder and the projection of said outer cylinder, the second of which extends between the external projection of said second intermediate cylinder andtthe internal projection of said first intermediate cylinder, and the thirdof which extends between the projection of said inner cylinder and the internal projection of second intermediate cylinder; a first tubular member having one end fixed to the base of said first intermediate cylinder, slidably extending through the base of said second intermediate cylinder and having an open end received in the enclosure in said, inner cylinder; a second tubular member having one end fixed to the'base of said second intermediate cylinder, slidably extending through the bore in the base of said inner cylinder in surrounding relationship about said first tubular member, and having an open end received in the enclosure in said inner cylinder; the external projection and the base of said first and said second intermediate cylinder defininga first and a second channel constituting communicating passages between said first annular space and the interior of said first tubular member, and between the second annular space and the interior of said second tubular member, respectively; said third annular space communicating with the enclosure in said inner cylinder through the aperture in the mantle of said inner cylinder; thebases of said cylinders defining therebetween three pressure chambers, the first of which is disposed between the bases of said outer and said first intermediate cylinder, the second of which is disposed between the bases of said first and said second intermediate cylinder and communicates with said first pressure chamber through said bore in the base of said first intermediate cylinder, and the third of which is disposed between the bases of said second intermediate and of said inner cylinder and communicates with said second pressure chamber through said bore in the base of said second intermediate cylinder; a source of pressure medium; and conduit means for connecting said source with said first annular space and with said first pressure chamber.

6. A double-acting, multi-stage hydraulic jack comprising, in combination: an outer cylinder having a base, a mantle, an open end and an internal projection adjacent to said open end; an inner cylinder having a base defining a bore, an external projection disposed about said base, a closed end, a mantle defining at least one aperture, and an enclosure therewithin; a first intermediate cylinder and a second intermediate cylinder, each intermediate cylinder having a base defining a bore, an external projection surrounding its base, a mantle, an open end, and an internal projection adjacent to its open end; the external projection and the mantle of said first intermediate cylinder being slidably received in the mantle and in the internal projection, respectively, of said outer cylinder, and the external projection and the mantle of said second intermediate cylinder being slidably received in the mantle and in the internal projection, respectively, of said. first intermediate cylinder, the external projection and the mantle of said inner cylinder being slidably received in the mantle and in the internal projection, respectively, of said second intermediate cylinder; the mantles of said cylinders defining therebetween three annnlar spaces the first of which extends between the external projection of said first intermediate cylinder and the projection of said outer cylinder, the second of which extends between the external projection of said second intermediate cylinder and the internal projection of said first intermediate cylinder, and the third of which extends between the projection of said inner cylinder and the internal sleeve of said second intermediate cylinder; a first tubular member having one end fixed to the base of said first intermediate cylinder, slidably extending through the base of said second intermediate cylinder and having an open end received in the enclosure in said inner cylinder; at second tubular member having one end fixed to the base of said second intermediate cylinder, slidably extending through the bore in the base of said inner cylinder in surrounding relationship about said first tubular member, and having an open end received in the enclosure in said inner cylinder; the external projection and the base of said first and said second intermediate cylinder defining a first and a second channel constituting communicating passages between said first annular space and the interior of said first tubular member, and between the second annular space and the interior of said second tubular member, respectively; said third annular space communicating with the enclosure in said inner cylinder through the aperture in the mantle of said inner cylinder; the bases ot said cylinders defining therebetween three pressure chambers, the first of which is disposed between the bases of said outer and said first intermediate cylinder, the second of which is disposed between the bases of said first and said second intermediate cylinder and communicates with said first pressure chamber through said bore in the base of said first intermediate cylinder, and the third of which is disposed between the bases of said second intermediate and of said inner cylinder and communicates with said second pressure chamber through said bore in the base of said second intermediate cylinder; a source of pressure medium; a valve housing; a supply pipe for connecting said source with said housing; a first conduit for connecting said housing with said first annular space; a second conduit for connecting said first pressure chamber with said housing; a discharge pipe connected to said valve housing; first valve means in said housing for controlling the fiow of pressure medium from said supply pipe into said first conduit; second valve means in said housing for controlling the flow of pressure medium from said supply pipe into said second conduit; and third valve means in said housing for controlling the flow of pressure medium from said second conduit into said discharge pipe.

7. A double-acting, multi-stage hydraulic jack comprising, in combination: an outer cylinder having a base, a mantle, and an open end; an inner cylinder having a base, a mantle defining a bore, a closed end, and an enclosure therewithin; a plurality of intermediate cylinders of progressively diminishing diameters slidably received in each other, each intermediate cylinder having a base defining a bore, a mantle, and an open end, the largestdiameter intermediate cylinder being slidably received in the outer cylinder and the smallest-diameter intermediate cylinder slidably receiving said inner cylinder; the mantles of all said cylinders defining therebetween a plurality of enclosed annular spaces, one about each intermediate cylinder and one about said inner cylinder, said last mentioned annular space communicating with said enclosure through the bore in the mantle of said inner cylinder; a tubular member connected to the base of each intermediate cylinder and slidably received in the base of the adjacent smaller-diameter intermediate cylinder, each tubular member having an open end extending into the enclosure in said inner cylinder when the jack is collapsed; the base of each intermediate cylinder defining a channel constituting a communicating passage between the interior of the tubular member connected to the respective base and the annular space surrounding the mantle of the respective intermediate cylinder; the bases of all said cylinders defining therebetween a plurality of pressure chambers each of which communicates with an adjacent chamber through the bore in the base of the respective intermediate cylinder; a source of pressure medium; and conduit means connecting said source with the chamber between the bases of said outer cylinder and of the largest-diameter intermediate cylinder, and with the annular space between the mantles of said outer cylinder and of the largest-diameter intermediate cylinder.

References Cited in the file of this patent UNITED STATES PATENTS 2,438,285 Houldsworth Mar. 23, 1948 2,517,153 Wood Aug. 1, 1950 2,783,744 Tennis Mar. 5, 1957 FOREIGN PATENTS 281,230 Switzerland June 3, 1952 

